Ultra high frequency control system



Feb. 18, 1947. M. D. FlsKE 2,416,168

ULTRA- HIGH FREQUENCY CONTROL SYSTEM I Filed Sept. 1'7. 1942 Milan D. Piske,

b Wwf. MAM

s His Attorneg.

Patented Feb. 1S 1947 UNITED STATES "PATENT oEEicE ULTRA man FREQUENCY CONTROL y sYs'rE Milan D. Fiske, Schenectady, N. Y., assignor to General Electric Company, a

New York corporation of Application September 17, 1942, Serial No. 458,671

7 Claims. (Cl. 179-1715) In order to eiect the propagation of elec- 2 It is a further object of'my invention ,to pro vide new and improved apparatus including electronic control devices associated with a resonant aperture positioned within a dielectric wave guide for controlling the wave propagation characteristics of the guide.`

B'rieiiy stated,`in the illustrated embodiments of my invention Iprovide new and improved arrangements for controlling thel propagation of electromagnetic waves through dielectric wave guides, and which are improvements of the type of systems' disclosed and broadly claimed in my Acopending joint patent application Serial No.

mum frequency which isdetermined largely-by the character of the waves being transmitted, the dielectric constant of the medium within the guide. and the transverse dimensions of the guide.

The types o1' waves which may be transmitted dielectrically through 'guides of this nature .are manifold and have heretofore been classified generally intothe E and H types. l In the E type waves. the electromagnetic waves have both longitudinal andy transverse components of electric netic field. ,I Bylusfe;l of the word transversefis meant transverse tofjthe direction oiwave propagation throughrtheguide. In the Hntypewavea the electromagneticwaveshaver both rlongitudinal and-transaerseomponents oifmagne'tlc' field but onlyatransverse componentof'electric field. The waves/which may be ,transmitted through guidesofthisznature have been `identi"` fled by ythe use ofthe; subscripts as'. indicated,L -En,m and Ham.;y 'I'he subscript nindicates the ,order of the wavevand the subscript m indicates themode of .propagation'vgv AThe order 'of the .wave is determined byf, the manner, in which the eld intensity varies circumferentially around the axis o'f the guide, whereas themode isdetermined by `the* manner of 'its variation Awith distance from the axis of; the guide. 'Although' hereinafter in v the discussion 'of my inventionan H01 type ofl l wave is referred"to, 'itis tovbe appreciatedthat my invention is applicablewith .equal facility to other H type'waves as well as to Eitype waves.

It is an object of my invention to; provide lnew and improvedfultra high frequencyicontrol ap-A paratus. i

It is another object of my invention to provide new and improved structuresiorcontrolling the propagation or 'attenuationof electromagnetic waves through dielectric wave guides.

458,670, filed September 17, 1942, .and which is assignedy tothe assignee of the present application. i l

In accordance with the yteachings 'of my invention described hereinafter, I provide new and improved electric discharge means to be used in conjunction with a tuned or resonant aperture which is positioned within or associated with lthe guide. The resonant aperture is provided in a transverse metallic wall which lies in aplane substantially transverse tothe direction of propagation of the electromagnetic waves through the Y guide, andV is tuned to the frequency 'of the ileld but only as transverse component of jmagexciting meansfto veflecta concentrationor acl centuation of Athepotential of the held-:incidentto. the propagation: of 'the electromagneticwaves `-through' the guide.` v IThe electric :discharge path the. propagationv oiy they electromagnetic. lwaves 'through theguide orvwhich 'effects modulationtofthe waves may comprise aicathode structure and associated grid .control meansV such as a Asingle In anothenmodiiicatio'n ofymy'invention; they -anode and cathode ofthe electric discharge path "may be arrangedA to vproduce av stream .of electuned or resonant aperture.

trons 'having adirection of movementsubstantially transverse or perpendicular to the direction of wave propagation, and may be positioned within the body of the transverse wall having the In accordance with a further object of my invention, I provide structure peculiarly adaptable n for use in the 4ultra highvfrequency ileld where it isdesired -to modulate the electromagnetic acteristic of ymy invention are set forth withy particularity in the appended claims. My` invention itself, however,v both as to its organi- I which controls zation and method of operation together with further objects and advantages thereof may best be understood by reference to the following description taken in connection with the accompanying drawing in which Fig. 1 is a perspective view, partly in section, of one type of system to which my invention may bev applied; Figs. 2 and 3 are, respectively, cross-sectional side and plan views of one modification of my invention; and Figs. 4 and 5 are, respectively, vertical cross-sectional and end views of a further modification of my invention. l l

There is a critical minimum frequency or cutolf frequency for each dielectric guide, the value of which is determined by the dielectric constant of the medium within the guide through which the electromagnetic waves are propagated and the transverse dimensions of the guide. Below this value of critical frequency, the electromagnetic waves are rapidly attenuated and the energy thereof is not transmitted an ap,- preciable distance along the axis of the guide. Above the critical frequency, the electromagnetic waves are propagated with an attenuation and velocity determined by the propagation constant be expressed as follows:

where a is the attenuation constant, and is the phase constant and both are real quantities whose magnitudes depend` upon frequency.

If the frequency is great enough, a is very small compared to ,B and waves are propagated without appreciable attenuation at a phase velocity which varies with the transverse .dimensions of the guide. When the excitation frequency is below the critical frequency, the Expression `1 may still be used but now a and ,8 both become imaginary with the result that f3 determines the attenuation and a determines the extent of wave o 45 tance along the axis ofthe guide for excitation action. Since below the critical frequency p is again much larger than a, the attenuation is very pronounced and the wave actionis very small. Physically, this means that transmission of waves through the guide is virtually non-existent at frequencies below the cut-E frequency.

Although my invention may be applied with equal facility to dielectric wave guides of various configurations, in the following discussion in order topresent some fundamental considerations relative to the description of my invention, the fundamental aspects will be described with particular reference to dielectric wave guides having' a rectangular cross section and wherein the height of the guide is a and the ,base is bg The phase constant 8 may be expressed:

where w is the angular velocity of the wave The wave length M of the electromagnetic waves propagated through the guide may be defined as:

10 increases as either n or m is increased, that is as the order of the wave becomes larger. Furthermore, it will be noted that as Aeither dimension a or b of the wave guide is decreased, the critical frequency increases. In addition, it should be noted that the critical frequency may also be decreased by increasing the value of the dielectric constant or by employing a material having a larger dielectric constant.

In order to simplify still further the presentation of the subject matter of my invention, it will be assumed that the dielectric is air and the sys-A tern is arranged for the transmission of an Hoi type wave where the electric component of the field is perpendicular to b, in which case the phase constant and critical frequency expressed by of the guide. This propagation constant P may Equations 2 and 3 become:

w#tizi-en where c is the ve1oc1ty of light in air,

The electromagnetic Waves are propagated through the guide;. that is, the expression for the progressive wave may be expressed as a function of the propagation constant and time. The electric intensity E and the magnetic H eld may be expressed as follows:

An inspection of the Equations '1 and 8 indicates that for given values of which is the dis- Referring now to Fig. 1 of the accompanying drawing, I have there diagrammatically illustrated one type of system to which my invention may be applied. The system comprises a dielectric wave guide of the hollow-pipe type having a rectangular cross section and provided with a base member I of transverse dimension b and a top plate member 2.

These members, which comprise a confining 1 and directional chamber for' the electromagnetic waves, are preferably constructed of a highly conductive material, such as brass or copper. The sides may be provided by plate members 3 and 4 having a height dimension a and are also con-v structed of a highly conductive metal. "One end propagated through the medium (w=21rf, where f 65 of thev guide may comprise a metallic plate 5 isthe frequency of the Wave), a1 is the permeability `of the medium, and e1 is the dielectric constant of the medium. The quantities n and m are, of course, the order and mode of the parwhich is conductively connected to the top, bottom and side members.

The wave guide may be completely enclosed by utilizing another end member 6 of conductive maticular wave being transmitted through the guide. terial, or may be open to the atmosphere and ter- The critical frequency fo may be dened as follows: l

feter-sieri* minated in a suitable radiator. Electromagnetic waves are established within the guide by suitable input electrode` means which may take the form of a concentric or coaxial transmission line comv prising a, tubular conductor 1 and a concentric conductor l. the former of which is conductively connected to base member I and the latter of Il. .The evacuation of their-asien donned vtherc- E by may be obtained by employinga suitable tubu-r which may be conductively connected to the top plate 2. It is to be appreciated that other forms of input electrode means, such as probes and the llke.`mayfbe employed inplaceoi' the concentric transmission line. and the character of the input electrodemeans is detenninedby the type oi' l electromagnetic .waves Which iti is desired to be extracted `from the guide by output electrode-` means which may also yt'alxethe iorm of a concentrictransmission -line having an outer tubular` conductor and-a concentricconductor I0. Conducten! maybe conductively connected to the top plate member 2. f r x The system to which my .invention is particularlyapplicablealso includes within the guide or associated therewith a`wall II lyingy in a .plane substantially transverse to the direction of wave '1'5" terior oi' thel cylinder II.- base; I,. and conductor,I`0 .maybe connected to the ,end ofthe cathodecylinder` Ilm'ay be supported propagation through the guide, and which is constructed of a highly conductive material such as brass or copper,.th`e wellbeing in physical contact with thetop, bottom and sides of theguide.

' A resonant aperture or slot I 2A isprovided in thel wall IIl and has an appreciable dimension transverse to the electric component E of the elec,- tromagnetic eld due to the waves transmitted through the guide. The resonanty aperture may be ofthe typel which comprises a central or elongated slit terminated at each end in circular openings I3 and I 4. The resonant aperture is tuned to' the frequency of the electromagnetic waves.

that is the frequency of the input electrode means,

for effecting a concentration of the potential due to the field of the waves within the guide. This concentration oi' potential is dueto the resonant characteristics ofthe aperture.

The dimensions ofthe resonant aperture I2, that is the .eil'ective height and length thereof, are determined by the excitation frequency, of the guide and thetransverse dimensions thereof.

Figs. 2 and l:i diagrammatically illustrate one embodiment of my invention which may bezemployed in connection with a resonant aperture used in connection with or associated with a-dielectric wave guide. More particularly, I provide means for establishing within the region of the tuned aperture or slot a controllable space charge which controls the effective dielectric constant of the medium surrounding the aperture and the effective dielectric constant of the medium within the guide through which the waves pass. A reference to Equations 2 and 3 above indicates that the phase constant and the critical frequency fo or functions of the dielectric constant of the medium through which the waves are propagated. Furthermore, it will be noted that the critical frequency increases as the eiective dielectric constant of this medium decreases.

In Figs. 2 and 3 I disclose arrangements whereby the space charge is controllable and whereby lation which maybe :sealed 'oil after evacuation.

Lametal coatedwith `analkaline earth metal or oxide thereoffin.v order to providea cathodejsurfaceof desiredemissiiliti AA *heating `velelne'x'ii': Il" y Y is provided-fertile cathodeandfmily be embedded-4 Withlnl'sllltable material placed Withil'h "l ported 'from the side' I Vwalls!y 4 by, means of .ametalliccircular collar I9 and a concentric vitreous'i nsulator 2M'` theI latter. of whichma'y extend an appreciable Cathode I1, may, .be su tional purpose vo1' impressingiacontrol potential on cathode I1. The cathode heating leads 22 may be made externally accessible byl extending through a glass bead insulator 23 which with a flanged lmetallic cylinder 2l constitutes a seal.

I provide a single wire grid 25 which is preferably parallel to the .principal dimension of the resonant slot I I and which.ismaintained in spaced relation with the cathode I1 and the resonant aperture.'v This element is preferably Aof a length equal to or greater than the principal dimension of the resonant aperture, and one end thereof may be embedded or anchored in the glass insulator 2|. The otherend'o! ,the single wire grid 25' is also sealed in the glass bead 23 and made externally accessible for -control purposes.

Y A suitable source oi' current, such as a battery 26, may be employed for supplying heating current to element I 8 and the voltage i'or the electric discharge path, constituted by theplate I I and the cathode cylinder I1, may be furnished by a suitable source such as a battery 21 which is connected to impress a relatively positive potential on the structure including the wall I I.

` The magnitude of the space charge is-controlied by controlling the potential difference between thecathode cylinder Hand `the wire 25, and

this potential difference may be effected by any suitable control signal which, for the purposes of illustration, is represented as'a source of alternating current 28.. It is to be understood that this source may be of any desired nature, either intermittent or periodic, and may be of low, high or intermittent frequency.

In operation, control of the potential of grid wire 25 determines the magnitude 'of the space charge, and. by a suitable choice of the range of signal potential the electron flow may be completely interrupted. The wave propagation characteristics of the guide, as explained above, are determined iria measure 'by the density of the space charge. .Within the purview of my invention,- the system maybe operated .by establishing a space charge which changesthe guide from a propagator to an attenuator, or the -space charge may be varied throughout limits which lie above that value of space charge which completely attenuates the waves within 'the' guide.

While in the specific descriptionvof my invention I have chosen to describe the electric dischar-ge means which produces the region of charged particles as. being one which produces a Referring now to Fis. 3,51 provide a'cathode, such asa thermio'nic cathode, comprising a me- .i tallic cylinder I 'I` in-spaced. relation 'with the wall v I I and more particularly-with respect to thel tuned ,aperture I2. The cylinder [lis-preferably otras" length equal to or greater than `the lengthjof'the Y resonant aperture :I2 and may be constructed of.

7 i stream or beam of electrons, it will be appreelated that I contemplate the provision of electric discharge means for 'establishing within the vicinity of the resonant slot or aperture a region of charged electric particles. For example, I may also employwithin the purview of my invention electric discharge means comprising a gas or vapor which is capable of ionization and which may be controlled by suitable means such as electrostatic controlmeans forv initiating the establishment of the ionized condition of the ls prising the wall Il, which operates as an anode, the cathode cylinder 29 and the grid 31 function as a controlled discharge path, the potential difference between grid 31 and the cathode cylinder 21 determining the magnitude or density of the space charge. This potential difference may also be derived; as illustrated in the drawing, from a signal source such as the source 28 to vary the potential cyclically and, if desired, grid 31 and grid wire 25 may be varied simultaneously in potential,

A further modiilcation of my invention is illustrated in Figs. 4 and 5, Fig. 4 being a vertical cross sectional view and Fig. 5 being an end view.

'Ihe arrangement of my invention illustrated in Fig. 4 vmay also be applied to a system such as that'shown in Fig. 1. More particularly, the con- Mtrolled electric discharge path for the resonant aperture in this modication of my invention is illustrated as producing a stream of electrons the direction of motion of which is transverse or perpendicular to the direction of wave propagation through the guide.

volume, the square of the unit charge of each particle and inversely proportional to the mass of each charge and some function of the field.

i It will be apparent that my invention may be. applied to numerous types of dielectric wave guides or modifications of apparatus using dielectric wave guides. For example, my invention may be applied to systems wherein it is desired to amplify or phase modulate the electromagnetic waves through the guide.

1 It will be apparent that apparatus built in accordance with my invention may also be employed as a controllable filter for guided waves.

The structure which produces the resonant aperture 38 may comprise right-angle anges of top members 39, 40 and bottom members 4I,

, 42 of two sections of a metallic wave guide. A1-

ternatively, the metallic structure or transverse wall which includes the resonant aperture may be constructed of solid pieces of metal welded to the two sections of the guide. If desired, of course the entire structure may be positioned 1 or enclosed within a sealing chamber so that 1 the surrounding atmosphere may be reduced to The aperture reects waves of all frequencies other than those in the region about the resonant frequency of the aperture. i

1 Fig. 3 also shows an alternative arrangement f a grid structure which may be employed as the control means for the electric discharge path. A cylindrical cathode 29 may be "supported in spaced relation with respect to wall Il and aperture I2 in a manner similar to that explained above in connection with cathode cylinder I1.

the desired pressure.

4I provide an Vanode' structure for the electric '/discharge path which may comprise an anode 43 of solid material, preferably of circular crosssectional area', which is arranged to lie within the body of the wall constituting the transverse dimension of the structure, The anode 43 is preferably insulated by an insulating cylinder 44 and i the entire anode structure may be supported by that is, may be supported by a metallic collar member 38 .which is welded or soldered to the side wall 3 and an insulating cylinder orA ro'd 3| which extends into and is supported at one end by collar 30 which itself extends into one end of the cylinder 29. The cathode in this instance may'also be of the thermionic type and may be heated by a heating element 32. The other end of cylinder 29 may be supported by a rigid lead-in conductor 33 which is conductively connected to cathode 29 and is made externally accessible by extending through a sealing structure comprising a vitreous glass insulator 34 anda flanged cylinder 35, the latter of which may be welded or soldered to wall 4.

A single wire or conductor 36 is positioned to lie substantially parallel with cylinder 29 and one end thereof may be embedded in the insulating rod 3|, the other end of which may extend insulating vitreous spacer and seal 41.

a metallic cylinder 45 which is welded to the anode 43. The whole anode structure may be supported from the top of the wave guide by means of a iianged cylindrical collar 45 and an The cathode structure may also be positioned within the body of the transverse wall and may comprise a thermionic cathode 48 of inverted cup shape within which a cathode heating element 49 is provided. 'Ihe cathode 48 is maintained l the modulation of the electromagnetic waves through and be sealed in the glass insulator 34. l

through the guide may be controlled at ultra high frequency by controlling. the eiective potential diierence between the anode 43 and cathode 48. Consequently, I provide a concentric or coaxial transmission line comprising an outer conductor 5l and an inner conductor 52, the latter of which extends to the vicinity of, but does not engage, vthe cathode 48. It will be appreciated that inasmuch as the spacing between the inverted cup 48 and the tubular conductor 52 is very small, these members are effectively connected together so far as the high frequency circuit is concerned. The modulating potential may be impressed between conductors 5I and 52 by any suitable agency and this agency is represented diagrammatically as element 53 in the drawing.

The cathodev structure is also sealed so that grid 58.

audios A9 the region 'within which thceiectric discharge takes place may be maintained at :necesiten-inw.

pressure. and this may. by may playing a glass annularffiil'sulator'l which/inf sealedfto -conductor andthe bottom plates 4l and 42 by means of a metallic. l'collar 5I. The" conductors for the element "491 g may extend through a part ofthe length., or the" entire length, oi the. inne'rf'oonductor 52 otfthei:

coaxial on line., 'A source otcathode heating current', such as" a battery-"56; may 'be A source of unidirectional'voltage, such'as a Y battery b1, 'may be employedfor impressing a relatively positive potential-on the anode 4 1, Oi' coursehitjis not necessary'for the utilization o! my invention toemploy for anode energization.

A grid 58 may be placedwithin the electric. discharge path provided by anode 43 and'cathode 18. Grid 58 may be welded or soldered to the ay unidirectional voltage.

transverse wall and extend substantially the entire length of the intermittent slot portion of the resonant aperture shown in Fig. 45. This grid4 may bejcoextelfsive with the anode transverse area and may be employed asa potential equalizing means for the electron stream. In addition,

- tion of electromagnetic waves through said guide this grid will also serve'to 'maintain `the desiredl 'i resonant characteristics of. theresonant aperture assembly.v

It will be noted by referring to Fig. 4 that the cathode 48' is spaced some distanceffrom the This particular conilgu'rati'on of the elements and spacing thereof also assists in assuring that `the resonant aperture maintains. with or.

assigned reference numerals corresponding to the elements shown in Fig. 4.

In operation, the embodiment of my invention illustrated in Figs. 4 and 5 functions in substantiaily the same way as that explained above in connection with Figs. 2 and 3. 'I'he density of the space charge controls the propagation characteristics of the wave guide, the effective dielectric constant of the medium surrounding the guide being decreased as the electron stream density increases. In this way, the electromagnetic waves are modulated. While I have shown and described my invention as applied to particular systems. embodying various devices diagrammatically shown, it will be obvious to those skilled in the art that changes and modiilcations may be made without departing from my invention, and I, therefore,aim in the appended claims to cover all such changes and modiiications as fall within the true spirit and scope of my invention.

What' I claim as new and desire to secure by Letters Patent of the United States is:

1. In combination, a dielectric wave guide of .l

the hollow-pipe type comprising two metallic sections, exciting means for establishing electromagnetic waves within one of said sections, an electric discharge meansffor producing a region of charged particles to control the wave propagation characteristics of said guide and including an anode and a cathode, a metallic wall structure lying in a plane substantially transverse to the direction of wave propagation of electromagnetic vthe hollow-pipe type comprising a through said guide` and formed to provide aresonant aperture tuned substantially to frequency oi-.said excitlngmeans and housing-said anode and said jcathode,. and

:trolling said electric discharge means. 2. Infcombination. a dielectric. waveguide. of

with` a resonant aperture tuned substantially to the frequencyof said exciting means, said wall structure substantially enclosing said anodeand said cathode, and. means' for controlling the density of saidcharged particles.

3. In combination, a dielectric wave guide -of thehollow-pipe type, exciting means for establishing electromagnetic lwaves within .said guide,

a metallic wall structure lying in a plane substantially transverse to the direction of propagaand having therein a resonant aperture tuned tothe frequency of the' exciting means. electric discharge means within the body of said wall for producing `a region of charged particles across said aperture and comprising an anode structure electrically insulated-from said wall and a cath= `.ode structure also within the body of Vsaid wall and electrically insulated therefrom. and means for controlling Athe potential difference between lishing electromagnetic waves within said guide..

a metallic wall within said guide'and lying in a planev substantially transverse to the direction of wave propagation therethrough and having therein a resonant aperture tuned substantially to the frequency of said exciting means, electric discharge means lying within the body of said wall and comprising anode and cathode structures lying within the body of said wall and spaced on opposite sides of the principal dimension of said "aperture,` and means for controlling the diierence in potential between said anode and said cathode to vary the density of said charged particles for modulating the electromagnetic waves.

5. In combination, a dielectric wave guide of v the hollow-pipe type, exciting means for establishing electromagnetic waves within said guide, a metallic Wall Within said guide and lying in a plane substantially transverse to the direction of wave propagation therethrough and comprising a resonant aperture tuned substantially to the frequency of the exciting means, electric discharge `means for producing a region of charged electric particles' substantially` transverse to the.

direction of wave `propagationand including an .insulated anode structure von one sideV ofthe principal dimension of said aperture 'and lying within the body of said wall and cathode structure on the opposite side of said aperture and also lying Within the body of said wall and insulated therefrom, and means for 'controlling the diiference of potential between said anode struc- Y ture and said cathode structure for controlling the propagation oi waves through said guide.

,meanstor connairofmetallicg, section ameans for establishing electromagnetic' `waves ones'section of'fsaidguide,. an.- electric discharge device comprising an anode 'and y a-:cathode for producing a region of charged particles for controllingthe wave propagation characteristics'ioi said guide, a metallic wall structure lying. in a plane substantially transverse to .the .direction of `Wave propagation of.electro-- magnetic waves through said guide yand provided 1i v 6. In combination, a. dielectric wave guide of the hollow-pipe type, exciting means for establishirigl electromagnetic waves within said guide,

guide, and a high frequency concentric transmission line one conductor of which is connected to said guide and the other conductor of which is connected tosaid. cathode for modulating the electromagnetic waves transmitted through said guide. t

'7. In combination, a dielectric wave guide of the hollow-pipe type, exciting means vfor establishing electromagnetic waves within said guide, a metallic wall'within said guide lying in a plane substantially transverse to the direction of wave propagation therethrough and comprising a resolnant. aperture tuned substantially to the frequency of said exciting means, electric discharge means for establishing a yregion of charged electric particles within the vicinity o! said aperture and comprising an anode structure lying within the body of said wall on one side oi! said aperture and a cathode structure lying within the body ot said wall on the opposite side vof said aperture, and externally accessible high frequency conducltor means connected to said cathode and lying within the body of said wall.

REFERENCES CITED The following references are of record in the le 'of this patent:

s'rATEs'PA'rEN'rs y Number Date l Name v 2,106,770 Southworth Feb. 1, 1938 FOREIGN PATENTS Number Country Date lAustralian Oct. 22, 1941 

